Helicopter flight control systems and other apparatus frequently include control rods with self-aligning bearings at the rod ends, to transmit linear movements via the rods to bell cranks or other mechanisms. Typically, the bearings are spherical in order to provide uniform surfaces to receive thrusts moments from a number of directions. Such spherical bearings are usually retained in an aperture described by peripheral side portions of the rod end which surround the bearing and provide a bearing retention socket which describes a portion at least of a spherical cavity. The bearing can then move freely within the rod end, without becoming disengaged therefrom.
While providing for large angular control motions, such control rod-end structures may also allow motion in other directions to the extent that wear producing contact is made between primary rod-end structures. The devices of U.S. Pat. Nos. 2,487,989, 2,753,225 and 2,973,227 each have an inherent angular limit to the degree of roll-over which can occur. However, the limit is due merely to their construction, which precludes further angular rotation. For instance, if the rod is rotated about its longitudinal axis to its full extent, either the bearing race or the edge of the control rod will contact clevis. Such contact will produce wear degradation of those primary structural parts that could lead to rod end or clevis failure. There are no actual stop means preventing such contact.
Various attempts have been made to cope with this roll-over wear producing problem. Thus, it has been proposed to limit such rotational motion by machining a groove in the bearing face to receive a corresponding "tongue" formed on the inside of the bearing race. In this connection, reference is made to Johnson, U.S. Pat. No. 3,401,964. Another proposal is to provide an inner race having a flanged end for the spherical inner bearing race, so as to limit rotational motion by contact between the flange and an oblong inner peripheral surface machined in the outer bearing race. In this connection, reference is made to Sowatzke, U.S. Pat. No. 3,510,178. Other proposals include circumferential groove-pin, or abutment stop means for limiting rotational motion of spherical journal bearings while allowing other required motions. In this connection, reference is made to Pickering and Stitzinger, U.S. Pat. Nos. 185,188 and 1,562,130 respectively. Such prior art proposals have the disadvantage that they involve modifications to the bearings themselves. As a result of contact and resultant wear, the bearing may become weakened, with consequent limitations on the loads it may be able to withstand before failure. The bearings would also be special order bearings rather than stock items, leading to added cost and inconvenience.